1. Field of the invention
The present invention relates to a device for supporting a structure relative to a stationary floor and in particular, to an aseismic device which has resistance to earthquakes and can support a structure such as a computer which is sensitive to the shock and vibration of an earthquake.
2. Description of Related Art
At present, structures used for daily and industrial applications are wide ranging and include manufacturing machines, household electrical appliances, transportation equipment, etc. Some of them are particularly sensitive to the shock of an earthquake. It is the most basic object of a support structure having earthquake resistance (hereinafter referred to as aseismic support structure) to prevent the collapse of these structures when an earthquake occurs. Furthermore, equipment sensitive to the shock of an earthquake, for instance, electronic equipment, computers, measuring instruments and the like (hereinafter referred to as equipment) require that consideration be given not only to avoid destruction of their functions by the earthquake but also prevent the loss of data or a malfunction. Some of them observe the behavior during an earthquake and instantaneously perform a data calculation based on the result of the observation, and the above requirement is more severe in such equipment. Accordingly, they particularly need to be fixed to an aseismic support structure different from ordinary structures, or to a floor or the like by a highly earthquake-proof system.
An earthquake first causes a problem of the movement or turnover of equipment. The movement of equipment may cause the breakage of the connected cables or the contact with other equipment which further increases the possibility of a malfunction. Further, the turnover of equipment may physically destroy other equipment or cause an injury to workers. Moreover, the effect on the inside of the equipment by the seismic shock from the floor surface is very significant. For instance, stress may occur in parts within the equipment that can break the package or cause data errors, loss of data, or the like. In addition, there is a similar need in various production machines. If such production machines move or fall down when an earthquake occurs, the smoothness of the process is lost, which is very dangerous.
Generally speaking, since many cables are connected to the above mentioned equipment, the floor is double-structured for large-sized equipment. That is, on the stationary floor (slab) forming the bottom part, there are additionally provided free access floors at predetermined intervals, and a free wiring is secured by the use of the intervals. The inventors of the present invention disclosed a method in which a toggle bar is used to fix equipment on free access floors (Japanese Patent Application No. 7-42747). However, this method cannot cover equipment which are smaller in size and directly fixed to a stationary floor.
Conventionally, there have been several structures or methods for supporting equipment directly fixed on a stationary floor. The simplest way is to attach a caster to the equipment and place the equipment on the stationary floor. Typically, in this method, the caster is normally in a locked state because it is undesirable for the equipment to move during its normal use. The caster becomes movable if an earthquake occurs and an acceleration greater than a predetermined value is applied on the equipment, so that the energy of the earthquake is absorbed by the movement of the equipment caused by the caster. This method only requires that a caster, which is a small part, be attached to the bottom surface of the equipment, and thus it is the simplest countermeasure against earthquakes. In addition, this method is convenient for a change in the placement of equipment because the location of the equipment is not fixed. However, the maximum earthquake resistance of this method is about 0.4 G, which is low, and thus it cannot hold up under a large earthquake which produces a serious problem for the equipment. Furthermore, since there are problems of stress generation on the cables due to the movement of the equipment, and the turnover of the equipment, it is not appropriate as an aseismic supporting method. As an improved method, there is a method in which a pad is attached to the caster, and a method in which the equipment is fixed to a stationary floor by means of an adsorption disk, but these are also essentially insufficient from the viewpoint of resistance to earthquakes.
As a method for increasing resistance to earthquakes, there is a method in which equipment is directly fixed to a stationary floor (slab) or free access floor by means such as bolts. The former is also called a direct support type, while the latter is called an indirect support type. The direct support type can resist an acceleration greater than 1 G as earthquake resistance, and has an advantage that the movement and turnover of equipment does not occur. On the other hand, however, since the equipment is difficult to move once they are fixed, a long-term plan for the placement layout is required and the costs for the placement (e.g. construction cost) are also high. In addition, since the earthquake energy directly propagates through the stationary floor, a problem such as a malfunction is likely to occur in this method.
Accordingly, there is a desire for an aseismic support structure which provides sufficient earthquake resistance, overcomes the disadvantages of the above described structures and methods and is applicable to existing equipment.
It is an object of the present invention to provide an aseismic support structure which prevents equipment installed on a stationary floor from falling down or moving when an earthquake occurs. Further it is an object of the present invention to provide an aseismic support structure having earthquake resistance greater than 1 G and can suppress the seismic effect on equipment to a minimum.
Moreover, it is an object of the present invention to provide an aseismic support structure and system which is also applicable to existing equipment, requires no modification of the room where the equipment is installed and does not inhibit transferring or moving the equipment after installation.